Redeemable Noncontrolling Interests / Redeemable Partnership Units (Details of Redeemable Noncontrolling Interest Units) (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest
Class A common units, carrying amount	$ 979,509	$ 1,273,018
Series D cumulative redeemable preferred, carrying amount	5,428	5,428
Class A
Redeemable Noncontrolling Interest
Class A common units, carrying amount	$ 979,509	$ 1,273,018
Outstanding Partnership Units held by Third Parties	12,528,899	12,197,162
Preferred or annual distribution rate (in dollars per share)	$ 2.62
D16 Cumulative Redeemable
Redeemable Noncontrolling Interest
Series D cumulative redeemable preferred, carrying amount	$ 1,000	$ 1,000
Outstanding Partnership Units held by Third Parties	1	1
Par or stated value per share	$ 1,000,000.00
Preferred or annual distribution rate (in dollars per share)	$ 50,000.00
D17 Cumulative Redeemable
Redeemable Noncontrolling Interest
Series D cumulative redeemable preferred, carrying amount	$ 4,428	$ 4,428
Outstanding Partnership Units held by Third Parties	177,100	177,100
Par or stated value per share	$ 25.00
Preferred or annual distribution rate (in dollars per share)	$ 0.8125